In a horizontal solid-bowl centrifuge, solid-liquid suspension enters the bowl through a duct. During use, the bowl is filled up to the rim and the bowl is rotated around an axis at full speed thus creating a gravitational field in the rotating solid-liquid suspension. The gravitational force causes the heavier solid parts of the suspension to settle against the walls of the bowl. During this settling operation, no rinsing liquid enters the bowl through the cleaning in place nozzles and the peeling tube is positioned such that it does not dip into the rotating solid-liquid suspension. After the settling operation is finished, a layer of solids will be lying next to the cylindrical wall of the bowl. Then the peeling tube will be positioned to allow an opening of the tube to dip into the liquid layer on top of the solid layer, and the liquid is peeled off to the outside of the bowl by the impact of the passing liquid as the bowl rotates. The peeling operation stops just before the solid layer would be touched. The solid layer then may be removed by peeling operation at lower speed by means of the same tube or by a special “knife” cutting the solid into a mechanical conveying device.
After the solid-liquid suspension has been separated and removed from the bowl, it is necessary to clean the bowl. Cleaning of the bowl is usually done by spraying a rinsing liquid onto the walls of the bowl while the bowl rotates. Subsequently, a final cleaning is performed manually while the centrifuge is stopped and the door is opened. If a filtering sieve drum is used, cleaning in place is possible without opening the centrifuge.
To be able to clean a horizontal solid-bowl centrifuge in a manner that complies with good manufacturing procedure, the rinsing solutions used in the individual cleaning steps must be removed from the interior without leaving any residue. However, the process described above and used with conventional centrifuges does not meet good manufacturing procedure standards because the rinsing solutions are not completely removed. A residual layer of cleaning solution remains on an inside wall of the bowl, even after peeling with the peeler tube.